Mica splitting process and apparatus



April 1947- I H. H. BURTON 2, 19,056

MICA SPLIT'I'ING PROCESS AND APPARATQS 7 Filed Feb. 19, 1943 PatentedApr. 15, 1947 2,419,056

UNITED STATES PATENTOFFICE;

MICA SPLI TTING PROCESS AND APPARATUS Harry H. Burton, Worcester, Mass,assignor, by

' opposed surfaces.

- mesne assignments, to Aerovox Corporation, a

corporation of Massachusetts Application February 19, 1943, Serial-No.476,435

24 Claims.

This invention relates in general to mica splitting; more particularly,it contemplates the rapid and economical division or separation of booksor thin blocks of sheet mica, each into a number of thin films, such ascondenser splits or sheets, or, as desired, into still-thinnerfsplittings or mica flakes, such as are required for the manufacture ofbuilt-up board or plate mica. The present application is acontinuation-in-part of my copending application Serial No. 454,722,filed August 13, 1942.

I There have been numerous attempts to obtain mechanical splitting orfilming of sheet mica; however, the industrystill is wholly dependentupon lmife-splitting (a manual operation requiring the utmost inpatience and dexterity) for the commercial production of these extremelythin and delicate mic'a sheets or films. Occasionally, the wielder of asplitting knife encounters a book of mica which yields readily to thedesired filming or splitting, but in most cases, this knife-splitting,even for operators of long training and experience, is a, very slow andtedious operation; also, it has always been extremely wasteful of thematerial, since a great many films despite the most careful manipulationof the splitting knife, undergo scratching or fracture in the act ofpeeling them from the block or book, this being due not only to theveryfragile character of the material, but also, in'even greater measure, tothe wide and unpredictable variations encountered in the strength andresistivity to splitting of the natural bond or adhesion in thedifierent planes of cleavage of the material and in'different parts orzones of any givenplane of cleavage.

Numerous efforts have been made to overcome or to materially reduce thisbond or adhesion betweenthe layers orclaminations of sheet mica; onesuch treatment, for example, was to first heat the .mica to just underredness and then to quench it in water. Up to now, all such attempts atpro-Conditioningof the mica, to facilitate its splitting orfilming havemet with failure, due primarily to the inability of the water, or otherbath liquid emp1oyed,,to penetrate appreciably between the layers orlaminations, or to ventlon contemplates a. splitting or filmingtechnique or practice, made feasible in large degree by the aforesaidpreconditioning of the material, which not only eliminates the greatamount of waste and loss that inevitably occurs with knifesplitting, butenables the splitting or filming operations to be rapidly performed byunskilled operators' needing no more than a, few hours of training andinstruction-in contradistinction to the many months of practice andinstruction required to train an operator for knife-splitting.

Other and further objects and advantages of my invention will be madeapparent by the following detailed description thereof, taken inconnection with the accompanying drawings, in which Fig. 1 is asectional view, exemplifying a step by which the book mica isconditioned, according to my invention, for splitting or filming.

Fig. 2 is aperspective view, illustrating an implement employed by anoperator in the splitting or' filming :of book mica according to myinvention.

Figs. 3,4, 5, 6 and 7 are a series 01 line diagrams representing anoperatorfs successive manipulations of a mica book, relative to theimplement of Fig. 2, in securing splitting or filming according to myinvention.

Fig. 8 is a sectional view of an implement similar to that of Fig. 2,but equipped with adjustable means by which to predetermine thethickness of the successive films that are split ofi from the book.

Like reference characters refer to like parts in I the latter simplyillustrating a suitable receptacle I, filled to the level 2 with liquid,in which are submerged the books a, 3 of sheet mica. Preferably, but notnecessarily, such :books have previously been cut, trimmed and reducedin thickness to substantially the conditions under. which materiallyaifect-the strong bond betweentheir My invention, in one of-its aspects,contemplates a pre-conditioning ofthe book mica to facilitate itssplitting or filming; that does in fact materially break downandminimize this bond or adhesion, without harm to the delicate filmsthemselves, this treatment being based on my,

discovery thata remarkably widespread liquid they would be subjected toknife-splitting.

It has long been recognized in this art that the bond or adhesionbetween the laminations terial into thinv films, or still-thinnersplittings,

as the case may be. I have discovered, however,

that a very marked reduction in the strength of penetration between eventhemost strongly bondedifilmscan be obtained, bysoaking the books inawater bath containinga wetting agent or surface-active material ofspecial constituency .aridproperties. l In another of itsaspects myinthis bond is obtained by soaking the mica books or blocks, such asshown at 3, ,3, in a water bath containing in small quantity an organicwater-soluble wetting agent or surface-active go material at the typeexemplified by the aliphatic a very low value the interfacial tensionbetween water, mica. and air, thus to make the bath liquid capable ofpermeating, penetrating, and materially breaking down the strength ofthe bond 'or adhesion between the laminations of sheet mica in book orblock form; that is to say, a highly satisfactory bath for this purposecan be made by the addition of twenty-five drops of a dilute solution ofaerosol (aerosol O. T. to each quart of water. The bath may be improved,if desired, by the addition of a few drops of ammonia, the effect ofthis being to clean any fog or film from the surfaces of the thin micalaminations or sheets into which the book is readily divisible, ashereinafter described.

Prolonged soaking of the mica in the conditioning bath of my inventionhas no harmful effect whatsoever on the material, nor do the thin filmsor splittings into which the mica books are subsequently divided sufferanyimpairment of their di-electric strength, or the other properties,that render thin sheet mica so indispensable in the manufacture ofcondensers, spark plugs radio tubes, and other electric devices. But myimproved bath liquid does act very noticeably on blocks or books ofsheet mica submerged therein, to render them readily susceptible todivision into thin films and splittings; this action, unobtainable byany soaking of mica books in ordinary water and other liquids ofrelatively high surface tension, is possibly explainable on the theorythat my bath liquid, by virtue of its extremely low surface tension, isable very quickly to spread and penetrate through minute gaps, breaks,or weak zones of the bond in each plane of cleavage, the liquid thusseeping inwardly to attack the bond in its unweakened areas and toobtain its gradual disintegration. Whatever the action may be, it is afact that blocks or books of mica, after soaking in a bath of theabove-described character, are much less resistant to splitting orfilming; with some mica, only a relatively short period of soaking isrequired to effect a material breaking down of the bond between thelaminations, but with other mica where the bond is stronger to startwith, the soaking period may need to be of several hours duration beforethe bond is sufficiently weakened to permit of easy splittingor filming.In any case, I have found that the action of my conditioning bath isbest served by maintaining same at a fairly warm temperature, not,however, as high as the boiling point of the water or other liquidingredient of said bath.

Book mica which has been soaked or treated as above described for asufiicient period to materially weaken the strong bond or adhesionbetween its laminations, can of course be'divided and sub-divided by aknife-splitting operation that requires the exertion of much less forceon the part of the operator to push the knife through and between thelaminations of the material, thereby speeding up the operation anddecreasing to some extent the spoilage and fracture of the films. Buteven as thus made easier, such knife-splitting practice is alwaysfraught with the hazards of film fracture and scratching,

4 due to-the fact that the laminations of the book rarely present amathematically flat surface; these deviations from absolute flatness,though very slight and minute, make it very difficult to open up a planeof cleavage with the splitting knife without damaging or fracturing thefilm surfaces on one side or the other of said plane. Although myabove-described soaking of book mica is of substantial benefit inconditioning the mica for knife-splitting, its greatest usefulness liesin the fact that it renders themica susceptible to splitting or filmingby the novel technique or practice now to be described, which not onlyavoids the numerous inherent disadvantages of knife-splitting, butenables the books to be rapidly divided and sub-divided withoutappreciable waste by operators having only a minimum of skill,experience and training.

Such new splitting or filming technique or practice is based onequipping each operator with one or more implements or devices of thecharacter depicted by Fig. 2, such implement or device, designated as-awhole by the numeral 4, being a hollow body of any suitable materialsuch as metal, which is preferably secured to a table or bench 5 atwhich the operator works, and which presents as its working face aconvex surface 6.

Said surface 6 preferably faces the operator, and rises from the tablesurface 5 at a convenient distance from the edge thereof, the implementor device 4 being held in this position by any suitable means, hereshown as in the form of a tubular extension I, projecting from thebottom surface 8 of said implement or device 4, and received snugly in ahole or opening 9 of the table or bench 5 This tube 1 communicates withthe interior of thebody 4, and at its other end is connected, as by atube l0, with'any suitable source of vacuum, such as a suction pump orair exhauster, not shown.

Such partial vacuum or suction thus maintained interiorly of the hollowbody is made effective on its convex working surface 6 by suitable slotsor openings II, II in the wall l2 that provides said surface 6, thesesuction apertures or openings l I,

I I, as best shown in Fig. 2, being preferably a In the utilization ofsuch an implement or de- I vice for the progressive splitting or filmingof books orblocks of sheet mica, according to my invention, theoperator, either seated at or standing before the table 5, removes aconditioned mica book of appropriate size or area from the bath of Fig.l and presents it face foremost to the aforesaid suction zone or band ofthe surface 6, taking care only to see that the books face portion soopposed to and seized by the suction apertures is a portion which isrelatively close to an edge, or extremity of the book. The eflect ofsuch a presentation is for the book 3 to be seized and supported by thesuction, against the working surface 6, in substantially the tangentialrelationship indicated by th diagram, Fig. 3-that is. with its faceseized and held suctionally against relation to the surface 6,

the surface 6 only near the book's edge portion IS. the remainder ofsaid face and the opposite edge or extremity l4 of said book being inspaced because of the latters convexity. With the book's support thustransferred to the suction device or implement 4, as indicated by Fig.3, it only remains for the operator to exert a light thumb or fingerpressure against the book in the vicinity of its free edge 14; suchpressure, in the direction of the working surface Gas indicated by thediagram Fig. 4, procures a cleavage starting at edge [3 between thesuctionally-gripped surface lamination l5 and the book's remaininglaminations, the latter collectively retaining their flat or planarcharacter, and thereby peeling away gradually from the former (thesuctionally-gripped surface lamination I5) as the pressure forces thebooks edge l4 nearer and nearer to the surface 6, (see diagram Fig. 5).During this peeling action, the suctionally-held surface lamination I5being thin and flexible enough to conform itself to the curvature of thesurface 6, is supported and sustained by said surface. Thus, there is noappreciable strain or stress imposed on the lamination l5 by thispeeling-away from it of the fiat relatively rigid body I6 constituted bythe books other laminations.

That is to say, the above-described movement or manipulation is onewhich effects a gradual planar tilting or rolling of this rigid body,relative .to the curved surface 6, in such a manner that the relation ofvirtual tangency between its plane and the surface 6 is alwayspreserved, notwithstanding that the movement causes the zone of tangencyto shift progressively farther and farther away from its originalposition, i. e., the suction zone defined by the slits. I I, ll. Thus asthe book edge i4 comes nearer to the Surface 6, the D- posite edge l3 ofbody is all the time movingaway from said surface, giving opportunityfor the operator, at or about the stage depicted by Fig. 5, to seize thebody l6 between thumb and finger, to hasten the peeling away from thelamination 55 by an upward swinging movement, (see diagram Fig. 6),about a pivot or axis afforded by the contact or proximate contact, ofedge M with surface 6.

With the body 16 thus peeled awayand stripped clear from thesuctionally, held lamination 15, the latter (see diagram Fig. 7) isleftstanding alone against the surface 6, in position for ready removal,either by pulling it off said surface, or by a momentary release ofthe'vacuum to allow its drop by gravity into a convenient receptacle,not shown; such release or momentary breaking of the vacuum can beeffected in any convenient way, as by providing a suitable valve, notshown,

in the tube or connection H), for letting atmo's-' pheric air into theinterior of the device 4, upon being opened momentaril by the operatorsdepression of a suitably placed foot treadle, or the like.

As soon as any such separated lamination I5 is removed from the surface6, the operator simply re-presents the same book, in its slightlyreduced or thinner form Hi, to the suction apertures H, H, and repeatsthe above-described manipulation to obtain the separation of anotherexternal layer or lamination, and so on until the book by successiveseparations therefrom of its layers or laminations is completelydivided, or is reduced to a residue so extremely thin that the relativestiffness or rigidity needed for the abovedescribed manipulation is nolonger present.

6 However, the needed stiffness or rigidity is usually not lost oreliminated until the book residue has been reduced to a. thickness ofabout 1 or 2 onethousandths of an inch, thin enough, that is, for theresidue itself to constitute a mica film or splitting that is fully asuseful for many electrical purposes as any of the thinner films orlaminations into which the major portion of the book, in the mannerabove described, may have been previously divided and sub-divided.

Such filming operation involving, in effect, successive peelings away ofthe book residue from the layer undergoing separation (incontradistinction to knife-splitting where the layer und rgoingseparation is peeled away from the book) is a cycle of simplemanipulation that can be quickly imparted and taught to operators whohave had no previous experience in the handling of mica; with onlylittle practice, such operators are able to performthe manipulations sospeedily as to obtain a much higher rate of production of mica films andsplittings than can be obtained by an experienced knife-splitter;moreover, by my method of splitting, the waste or spoilage (which isalways very heavy with knife-splitting) is reduced to an almostnegligible factor. The material is successively presented to andmanipulated on the implement or device 4, always in the same way, by aroutine which is simple and easily learned; in fact, it is perfectlypossible for sheet mica, under the conditions and with. the equipmentcontemplated by my invention, to be split or filmed by blind operators,once they have been taught the hand movements that are involved. It willbe understood, of'course, that the implements or devices 4 willordinarily be provided in a variety of sizes, those of small size beingused with small area books, and those of larger size being used withlarge area books.

. Fig. 8 shows a suction device or implement, similar in constructionand operation to that of Fig. 2, but equipped with an arrangement bywhich to adjust or predetermine the thickness of the films that aresplit off in succession from the book material. For this purpose, theworking surface 6' of the suction device or implement 4 is formed justbelow the suction slits H, II with a small hole H, in which is slidablybut snugly received a stem E8, the latter at its outer end having anupward projection IS, in the form of a'small chisel-point substantiallyparalleling the surface 6 and of sufiicient sharpness to penetrate by aminute amount the edge of -a book or block of sheet mica, when thelatter, in the manner above described, is presented by the operator tothe suction slit H, H. The stem l8 at its other end is secured tothe'upper portion of a metal plate I 20, slightly spaced from the wallI2 except along its lower edge portion, the latter being anchored tosaid wall l2 as by means of screws 2|, 2|, or the like. At. anintermediate point, between its upper and lower portions, the plate 20'has a threaded hole receiving an adjusting screw 22 of very fine pitch,said screw 22 passing through thewall i2, with its head exposed on thesurface 6' 'to permit it to be manipulated for slight flexure's of theplate 20, thereby to vary 0 adjust adhesion between the laminations ofsaid material.

2. The herein described treatment of sheet mica in block or book form tofacilitate its splitting or filming, which consists in plunging the sameinto water containing a small percentage of a dioctyl ester ofsulfosuccinate the effect of which is to materially reduce the surfacetension of the water.

3. The herein described treatment of sheet mica in block or book form tofacilitate its splitting or filming, which consists in immersing thebooks in water containing a small amount of aerosol O. T. solution theeffect of which is to materially reduce the surface tension of thewater.

4. The herein described treatment of sheet mica in block or book form tofacilitate its splitting or filming, which consists in immersing thebooks in water containing a small amount of "aerosol O. T. 10%"solution, namely, twenty-five drops of said solution to each quart ofwater the effect of which is to materially reduce the surface tension ofthe water.

5. The herein described treatment of sheet mica i block or book form tofacilitate its splitting or filming, which consists in subjecting it toa water bath containing in solution a small amount of the wetting agentknown as "aerosoP and a few drops of ammonia.

6. In the art of splitting or filming sheet mica,

' the improvement which consists in holding a mica book in fixedposition, by suction applied to its face, against a'surface which fallsaway from the plane of said book, and then deflecting the book towardsaid surface, whereby to peel or strip it bodily from the suctionallyheld outside lamination thereof.

'7. In the art of splitting or filming sheet mica, the improvement whichconsists in supporting a, mica book in fixed position by suctioneffective on a limited area of the books face near one edge 8 10. In theart of splitting or filming sheet mica, the improvement which consistsin suctionally gripping and holding a mica book at a limited face areanear one edge in fixed position, and then tilting the plane of said bookabout a fulcrum between its free edge and the suctionally gripped facezone, to'strip said book bodily from its suctionally-held externallamination.

11. In the art of splitting or film sheet mica, the improvement whichconsists in suctionally gripping and holding stationary a mica book, ina limited face area near one edge, simultaneously engaging and piercingsaid edge in a plane of cleavage having a predetermined spacing from thesuctionally-engaged outside lamination of said book, and then tiltingthe plane of said book about a fulcrum between the books free edge andits suctionally-gripped face zone, to divide said book on said plane ofcleavage.

thereof, and then, by pressure against the free edge of the book,procuring a planar deflection thereof which strips it bodily from thesuctionallyheld lamination.

8. In the art of splitting or filming sheet mica, the improvement whichconsists in gripping and holding a mica book in fixed position near oneedge of its face by suction exerted through a surface which extends indivergent relation to the remainder of said face, and then subjectingthe sosupported book to planar deflection in the direction of saidsurface, to strip it bo'dily from the suctionally-held externallamination.

9. In the art of splitting or filming sheet mica, the improvement whichconsists in engaging a mica book in a limited area near one edge of. itsface with suction apertures, the latter being provided by a fixedsurface which stands in divergent relation to the remaining face area ofthe sosupported book, and then, by pressure against the free edge ofsaid book in the direction of said divergent surface, procuring a planardeflection to strip the sam bodily from the suctionally-held externallamination thereof.

12. A device for use in the splitting or filming of sheet mica,comprising a stationary body having suction apertures adapted to supportand hold stationary a mica book by contact with a face thereof near oneedge, said body providing a fulcrum for the planar tilting of said book,between the latters free edge and said suction apertures, and means onthe opposite side of said suction apertures from said fulcrum to piercesaid book edge in a plane of cleavage at a predetermined spacing fromthe suctionally-held outer surface area.

13. In the art of splitting or filming sheet mica, the improvement whichconsists in soaking each mica book in water containing an ester ofdicarboxylic or sulfodicarboxylic acid in sufficient amount to reducematerially the interfacial tension between water, mica and air, thensupporting and holding the so-treated book in fixed position by suctioneffective on the face of an external lamination, near one edge thereof,and finally, by pressure applied near the free edge of said book,procuring its planar deflection to strip it bodily from saidsuctionally-heldlamination.

14. In the art of splitting or filming sheet mica, the improvement whichconsists in immersing each mica book in water containing an organicwater-soluble wetting agent or surface-active material in suflicientamount to materially reduce the waters surface tension, prolonging suchimmersion substantially in proportion to the strength of the naturalbond or adhesion between the laminations of the book, procuring witheach so-treated book successive contacts with suction apertureseffective over a limited face area near one edge of said book, tostationarily support said book with its remaining face area in a, planedivergent from the surface containing such suction apertures, and,during each period of such support, urging said book toward said surfaceby pressure applied near its free edge, thereby procuring its planardeflection to strip the same bodily from the suctionally-held externallamination thereof.

'15. In the art of splitting or filming sheet mica, the improvementwhich consists in soaking each mica book in water containing a smallamoimt of aerosol O. T. 10% solution, thereby through the materiallylowered surface tension of said waterto obtain the latters penetrationbetween the laminations of said book, presenting the sotreated booksuccessively to suction apertures formed in a convex surface, tostationarily support said book, tangentially to said surface, by suctionexterted on the face of an external lam ination near one edge of thebook and in the and weaken period ofeach such support, producing thebook's planar deflection toward said surface, whereby to peel or stripit bodily from its suctionally-held external lamination.

16. In the art of splitting or filming sheet mica, the improvement whichconsists in soaking each book in amoderately heated water bathcontaining the wetting agent aerosol and a few drops of ammonia insuiiicient amount to materially reduce the waters surface tension,procuring successive supports of said book, by suction applied to itsface, near one edge thereof, against a surface which falls away fromsupported book, and in the instance of each such support, causing planardeflection of the book toward said surface, to peel or strip itbodilyfrom its suctionally-held external lamination.

17. In the production of mica films and splittings from book mica, theimprovement which consists in submerging the book material in watercontaining the wetting agent known as aerosol in sufiicient amount tomaterially reduce the water's surface penetrate any breaks or gaps inthe bond between the materials layers, prolonging such submergence asumcient time for the penetrant liquid to attack and weaken said bond,thereby to promote formation of cleavage planes between said layers,and-then splittingsaid material in said planes.

18. In the production of mica films and plittings from book mica, theconsists in submerging the book material in water containing the wettingagent aerosol in sufficient amount to materially reduce the waterssurface tension, thereby enabling it to penetrate any breaks or gapsinthe bond between the materials layers, prolonging such submergence asufiicient time for the penetrant liquid to attack said bond, thereby toestablish planes of cleavage between said layers, and then splittingsaid material on the planes of cleavage so established.

19. In the splitting or filming of book mica which has been previouslytreated to reduce the strength of the bond or adhesion between itslayers, the improvement which consists in repeatedly manipulating thebook material, to establish cleavages between its residue and thesuccessively-exposed external layers thereof, in the following sequenceor order, viz., (l) supporting the material in fixed position by suctioneffective on its face near oneedge thereof, against a surface whichfalls away from the plane of the so-supported material, and (2)procuring a planar defiection of said material toward said surface, toopen up a cleavage plane between the suctionally held face laminationand the remainder of said material.

20. In the splitting or which has previously been treated to reduce thestrength of the bond or adhesion between its layers, the improvementwhich consists in repeatedly manipulating thebook material, to effectcleavages between itself and successively-exposed surface layersthereof, in the following order or sequence, viz., (1) presenting a faceof the material near one edge to suction apertures provided by a fixedconvex surface, thereby to support said material substantially intangential relation to said surface, and (2) pressing the free edge ofsaid material toward said surface, thereby to open up a plane ofcleavage atthe opposite edge bethe plane of the sofilming of book micasented facewise tension, thereby enabling it to improvement which i0tween the suctionally-grlpped layer and the remaining layers.

21. Mica splitting apparatus, including a device having a generallyconvex surface and an adjacent aperture, means for exerting suctionthrough said aperture, and a projection adjacent said aperture andminutely offset from said surface in positon'to pierce the edge of amica book preto said aperture and held by said suction in substantiallytangential relation to said surface.

22. Mica splitting apparatus, including a device having a generallyconvex surface and an adjacent aperture, means for exerting suctionthrough said aperture, a projection adjacent said aperture and minutelyoffset from said surface in position to pierce the'edge of a mica bookpresented facewise to said aperture and held by said suction insubstantially tangential relation to said surface, and means foradjusting the offset of said projection from said surface.

23. In the splitting or filming of book mica, the improvement whichconsists in first soaking the books in a water bath containing anorganic water-soluble wetting agent whose effect is to materially reducethe interfacial tension between water, mica and air, then stationarilysupporting each book so-treated repeatedly by successive presentationsof its face, near one edge, to a suction aperture provided in a surfacewhich falls away from the plane of the so-supported book, and after eachsuch presentation procuring the planar deflection of the booktoward'said surface by finger pressure thereon at a point appreciablyremoved from said suctionally-engaged portion, whereby to strip thebook-residue bodily from the successive suctionally-held externallaminations thereof.

24. The herein-described method of splitting or filming book mica whichconsists in repeatedly presenting a book, for temporary stationarysupport by face engagement therewith, to suction means effective only onan edge portion of said face, and in each period of support, by fingerpressure exerted on said book at a point remote from its support zone,procuring its planar deflection, to initiate stripping or cleavage ofthe residue of book material away from the suction- The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 686,929 Heard et al Nov. 19,1901 1,194,155 Edgecomb Aug. 8, 1916 1,823,136 Frederick Sept. 15 19311,829,031 Atwood Oct. 27, 1931 1,870,835 Cofley et al Aug. 9, 19321,722,082 Frederick July 23, 1929 1,771,943 Tinnerholm July 29, 19302,306,292 Atwood Dec. 22, 1942 2,176,423 J aeger l Oct. 17, 19392,028,091 Jaeger Jan. 14, 1936 FOREIGN PATENTS Number Country Date12,570 British 1908 British Feb. 28, 1910

